- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Atomic and electronic structure of ferroelectric La-doped HfO<sub>2</sub> films
摘要： The atomic structure and optical properties of ferroelectric La-doped hafnium oxide (La:HfO2) thin films grown by the plasma-assisted atomic layer deposition were investigated. Using high resolution transmission electron microscopy, it was shown that the studied La:HfO2 film has a orthorhombic polar structure with the P mn21 space group. It was found that the film exhibits ferroelectric properties. By means of X-ray photoelectron spectroscopy and specroellipsometry it was established that La:HfO2 consists of the HfO2 and La2O3 phases mixture. The specroellipsometry analysis with the Bruggeman effective medium approximation showed that the investigated La:HfO2 consists of 88% HfO2 and 12% La2O3. It is shown that etching La:HfO2 with argon ions leads to the oxygen vacancies generation in the near-surface region. These vacancies are generated mainly due to the knocking out of oxygen atoms to the interstitial positions, and the following annealing at 700 ℃ in vacuum for 1 hour leads to the annihilation of that Frenkel defects.
关键词： ferroelectric,XPS,electronic structure,plasma-assisted atomic layer deposition,atomic structure,La-doped HfO2,specroellipsometry,HRTEM
更新于2025-09-23 15:21:01
-
Study of nanometer-scale structures and electrostatic properties of InAs quantum dots decorating GaAs/AlAs core/shell nanowires
摘要： The configurations of core/shell nanowires (NWs) and quantum dots (QDs) decorating NWs have found great applications in forming optoelectronic devices thanks to their superior performances, and the combination of the two configurations would expect to bring more benefits. However, the nanometer-scale electrostatic properties of the QD/buffer layer/NW heterostructures are still un-revealed. In this study, the InAs QDs decorating GaAs/AlAs core/shell NWs are systemically studied both experimentally and theoretically. The layered atomic structures, chemical information, and anisotropic strain conditions are characterized by comprehensive transmission electron microscopy (TEM) techniques. Quantitative electron holography analyses show large number of electrons accumulating in the InAs QD especially at the dot apex, and charges of reversed signs and similar densities are observed to distribute at the sequential interfaces, leaving great amount of holes in the NW core. Theoretical calculations including simulated heterostructural band structures, interfacial charge transfer, and chemical bonding analysis are in good accordance with the experimental results, and prove the important role of AlAs buffer layer in adjusting the heterostructural band structure as well as forming stable InAs QDs on the NW surfaces. These results could be significant for achieving related optoelectronic devices with better stability and higher efficiency.
关键词： quantum dot,transmission electron microscopy,atomic structure,core/shell nanowire,electrostatic property
更新于2025-09-23 15:19:57
-
Atomic structure of nanodiamond and its evolution upon annealing up to 1200?°C: Real space neutron diffraction analysis supported by MD simulations
摘要： Lattice strain, crystallite shape and the crystallite size distribution in nanocrystalline diamond were determined from powder diffraction data. The data were analysed by the direct space PDF method in combination with Molecular Dynamics simulations. Experimental Pair Distribution Functions were obtained from the large Q neutron diffraction data. Lattice strains were determined by comparison of the atomic pair distances at different length scales. The experimental pair-distance data were matched against the Molecular Dynamics models of diamond nanograins. Lattice relaxation at the surface and in the bulk of the simulated nanodiamond grains varied with their shape and size. Comparison of the model data to the experimentally determined strain characteristics yielded accurate information on the structure of the actual nanodiamond powders. In the as-synthesized nanodiamond the grains are polyhedrons predominantly terminated by (100) and (111) surfaces. Upon annealing the (111) surfaces with one dangling bond per atom graphitize and transform into surfaces with three dangling bond per-atom. In the samples annealed at 1200oC all grains are octahedrons terminated only by three dangling bond (111) surfaces. The mechanism of the atom rearrangement during the transformation of the (111) diamond surface into a graphite double-sheet was proposed.
关键词： graphitization,atomic structure,molecular dynamics,nanodiamond
更新于2025-09-19 17:15:36
-
Pb phases on Si(111)
摘要： We present here a combined experimental Raman spectroscopy and ab initio theoretical study of the (√3×√3) reconstructed SIC phase of Pb on Si(111) and discuss their relation to the atomic surface structure. The Raman response of the surface localized vibrational modes, in particular, is identified in the low-frequency spectral range (down to 15 cm?1). We demonstrate that Raman spectroscopy is a very powerful approach to test atomic structures of surfaces and a valuable complement to standard surface analytics. While the calculated spectra of H3 and T4 are too similar to allow a discrimination of these phases, the good overall agreement to the measured Raman spectra enables a classification of the observed vibrational modes.
关键词： surface vibrations,Pb/Si(111),atomic structure,ab initio,Raman spectroscopy
更新于2025-09-10 09:29:36
-
Investigation of the Atomic Structure of Ge-Sb-Se Chalcogenide Glasses
摘要： Glasses with composition of GexSb40-xSe60 (x= 40, 35, 32, 27, 20, 15 at. %) have been synthesized. Neutron and X-ray diffraction techniques were used to study the atomic glassy structure, and Reverse Monte Carlo (RMC) simulations were applied to model the 3-dimensional atomic configurations and thorough mapping of the atomic parameters, such as first and second neighbour distances, coordination numbers, and bond-angle distributions. The results are explained with formation of GeSe4 and SbSe3 structural units, which correlate with the Ge/Sb ratio. For all the studied compositions, the Ge-Se, Sb-Se, Ge-Ge, and Se-Se bonds are significant. RMC simulations reveal the presence of Ge-Sb and Sb-Sb bonds, being dependent on Ge/Sb ratio. All atomic compositions satisfy formal valence requirements, i.e., Ge is fourfold coordinated, Sb is threefold coordinated, and Se is twofold coordinated. By increasing the Sb content, both the Se-Ge-Se bonds angle of 107±3° and Se-Sb-Se bonds angle of 118±3° decrease, respectively, indicating distortion of the structural units. Far infrared Fourier Transform spectroscopic measurements conducted in the range of 50-450 cm-1 of oblique (75°) incidence radiation have revealed clear dependences of the IR band’s shift and intensity on the glassy composition, showing features around x=27 at.% supporting the topological phase transition to a stable rigid network consisting mainly of SbSe3 pyramidal and GeSe4 tetrahedral clusters. These results are in agreement with the Reverse Monte Carlo models, which define the Ge and Sb environment.
关键词： X-ray diffraction,chalcogenide glasses,atomic structure,FTIR spectroscopy,Ge-Sb-Se,neutron diffraction,Reverse Monte Carlo
更新于2025-09-04 15:30:14
-
Simultaneous Prediction of Atomic Structure and Stability of Nanoclusters in a Wide Area of Compositions
摘要： We present a universal method for the large-scale prediction of the atomic structure of clusters. Our algorithm performs the joint evolutionary search for all clusters in a given area of the compositional space and takes advantage of structural similarities frequently observed in clusters of close compositions. The resulting speedup is up to 50 times compared to current methods. This enables the first-principles studies of multi-component clusters with full coverage of a wide range of compositions. As an example, we report an unprecedented first-principles global optimization of 315 SinOm clusters with n ≤ 15 and m ≤ 20. The obtained map of Si-O cluster stability shows the existence of both expected (SiO2)n and unexpected (e.g. Si4O18) stable (magic) clusters, which can be important for miscellaneous applications.
关键词： atomic structure,nanoclusters,evolutionary algorithm,first-principles,stability
更新于2025-09-04 15:30:14